The present invention is concerned with improvements in driving mechanisms of a type in which clutch and/or brake components are immersed in a liquid bath during operation so as to provide for a dissipation of frictional heat away from such components during successive cycles of engagement and disengagement. The specific improvement of the present invention is one of injecting a gas into the liquid bath of known mechanisms of the type just described so as to reduce drag stresses which develop between spaced components moving relative to one another in the liquid bath.
It is known in the art to provide for clutch, brake, or combination clutch/brake units which include disc and plate components that are brought into successive engagement and disengagement to change a driving characteristic of the unit. It is also known to submerse the working components of such units in a liquid bath for the primary purpose of heat from the areas of engagement between the disc and plate components. Known devices of the type just described are fully illustrated and discussed in U.S. Pat. Nos. 2,998,872; 3,614,999; and 3,680,666, and in other prior publications showing similar arrangements. Reference may be made to these patents for a more complete understanding of the prior art devices with which the present invention is concerned, and the specifications and drawings of the above-identified patents are incorporated herein by reference to the extent necessary to supply background information and understanding to the present specification.
It has been found in the operation of machinery with known mechanisms of the type discussed above that a measurable and significant amount of drag develops between adjacent discs and plates when they are out of contact with each other but moving relative to one another in the liquid bath supplied for cooling them. In fact, it has been found, in certain applications of such mechanisms to forging presses, that the power required to overcome drag in the clutch/brake mechanism is many times that required to drive the machine itself, thus requiring the use of a considerably larger and more expensive drive motor than would otherwise be required to drive the machinery. This drag appears to develop as a result of shear stresses in the films of liquid as contained within the space established between moving components during the operation of mechanisms of this type, and it has been determined that the drag characteristic can account for a considerable consumption of power applied to the unit under consideration.
The present invention constitutes a relatively remarkable, but simple, discovery that the aforesaid drag problem can be alleviated, by as much as a factor of five, through a technique which involves the introduction of a quantity of gas, such as pressurized air, into the liquid bath in such a way that the air is entrained and contained within the body of liquid in the spaces which exist between working components of the unit.
Although it has not been determined exactly why the introduction of air into a liquid bath results in such a substantial reduction in drag, it is believed that the entrainment of air in the liquid bath substantially reduces the Kinematic viscosity of the oil medium so as to reduce its film shear stress, and that this is accomplished by "foaming" the liquid bath with the injected air. The foamed liquid retains nearly the same cooling properties for removing heat from the areas of engaging plates and discs in the device, and also, the foamed liquid functions as a lubricant for certain bearing surfaces contained within the device.
Thus, the apparatus of the present invention comprises a gas injecting means for introducing a quantity of a gas into a liquid bath to thereby reduce drag between components of a driving mechanism which are brought successively into and out of engagement with each other to change a driving characteristic of the mechanism.
The method of the present invention comprises, in its simplest form, the step of introducing a quantity of gas into a liquid contained within a clutch or brake unit, or combination thereof, of the type aforesaid.
These and other features and advantages of the present invention will be more completely understood in the detailed discussion which follows. In that discussion reference will be made to the accompanying drawing as briefly described below.